This invention relates generally to the field of cataract surgery and more particularly to a surgical parameters control method for use with a phacoemulsification system.
The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of the lens onto the retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and lens.
When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial intraocular lens (IOL).
In the United States, the majority of cataractous lenses are removed by a surgical technique called phacoemulsification. During this procedure, a thin phacoemulsification cutting tip is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting tip liquefies or emulsifies the lens so that the lens may be aspirated out of the eye. The diseased lens, once removed, is replaced by an artificial lens.
A typical ultrasonic surgical device suitable for ophthalmic procedures consists of an ultrasonically driven handpiece, an attached cutting tip, and irrigating sleeve and an electronic control console. The handpiece assembly is attached to the control console by an electric cable and flexible tubings. Through the electric cable, the console varies the power level transmitted by the handpiece to the attached cutting tip and the flexible tubings supply irrigation fluid to and draw aspiration fluid from the eye through the handpiece assembly.
The operative part of the handpiece is a centrally located, hollow resonating bar or horn directly attached to a set of piezoelectric crystals. The crystals supply the required ultrasonic vibration needed to drive both the horn and the attached cutting tip during phacoemulsification and are controlled by the console. The crystal/horn assembly is suspended within the hollow body or shell of the handpiece by flexible mountings. The handpiece body terminates in a reduced diameter portion or nosecone at the body's distal end. The nosecone is externally threaded to accept the irrigation sleeve. Likewise, the horn bore is internally threaded at its distal end to receive the external threads of the cutting tip. The irrigation sleeve also has an internally threaded bore that is screwed onto the external threads of the nosecone. The cutting tip is adjusted so that the tip projects only a predetermined amount past the open end of the irrigating sleeve. Ultrasonic handpieces and cutting tips are more fully described in U.S. Pat. Nos. 3,589,363; 4,223,676; 4,246,902; 4,493,694; 4,515,583; 4,589,415; 4,609,368; 4,869,715; 4,922,902; 4,989,583; 5,154,694 and 5,359,996, the entire contents of which are incorporated herein by reference.
In use, the ends of the cutting tip and irrigating sleeve are inserted into a small incision of predetermined width in the cornea, sclera, or other location. The cutting tip is ultrasonically vibrated along its longitudinal axis within the irrigating sleeve by the crystal-driven ultrasonic horn, thereby emulsifying the selected tissue in situ. The hollow bore of the cutting tip communicates with the bore in the horn that in turn communicates with the aspiration line from the handpiece to the console. A reduced pressure or vacuum source in the console draws or aspirates the emulsified tissue from the eye though the open end of the cutting tip, the cutting tip and horn bores and the aspiration line and into a collection device. The aspiration of emulsified tissue is aided by a saline flushing solution or irrigant that is injected into the surgical site though the small annular gap between the inside surface of the irrigating sleeve and the cutting tip.
Prior to use in surgery, the various handpieces, tubings and fluid management cassettes all need to be purged of air or primed. During the priming stage, current phacoemulsification systems also run an aspiration system diagnostic step to test for leaks or blockages in the aspiration system. During this diagnostic step, the system pump is activated to generate a certain vacuum in the aspiration line. If the system is not able to reach the desired vacuum level, this indicates to the system that there is a leak somewhere in the aspiration system, and the system will sound a warning for the operator. On the other hand, inability to release previously build vacuum indicates that there is a blockage in the system, such as a kink in one of the tubings.
Following the priming step, a flow check is performed specifically intended to verify an adequate fluid flow through the surgical handpiece. Current phacoemulsification systems use a small rubber test chamber that fits over the cutting tip and sleeve. The test chamber is filled with the irrigation fluid and when placed on the handpiece creates a closed compliant aspiration system. During this test an excessive vacuum level for a given pump speed would indicate a flow restriction in the fluidic path. Also, a manual check can be performed by the user to ensure that the test chamber is filled and pressurized upon test completion. A deflated test chamber would be an indication of the irrigation flow restriction.
While this priming and diagnostic system procedure is effective, it can cause some compromises with current phacoemulsification system technology. For example, phacoemulsification tip technology has evolved over the years and many different tip styles and diameters are now available. As will be understood to one skilled in the art, an aspirating tip with a small diameter or bore will naturally have a higher resistance to flow than a large bore tip. Therefore, at any given pump speed, a small bore tip will create a higher vacuum in the aspiration line than a large bore tip. As a result, diagnostic settings that use a vacuum level compatible with a small bore tip may not be appropriate when a large bore tip is used, and visa versa. This can lead to inaccuracies and false warnings by the system. Similar inaccuracies can result from different sized tubings and handpieces. Also, a reliance on the user to verify a proper test chamber state following the diagnostics completion is subjective and susceptible to a human error.
Therefore, a need continues to exist for a method of priming and testing phacoemulsification systems that is accurate for a wide variety of handpieces, tubings and tip.